This invention relates to particulate detergent or cleaning compositions that comprise only water-soluble constituents as their builder component and that contain specially coated alkali metal percarbonate particles.
Besides the surfactants essential to their detersive performance, detergents normally also contain so-called builders that support the performance of the surfactants by eliminating hardness salts, i.e. essentially calcium and magnesium ions, from the wash liquor, so that they do not interact negatively with the surfactants. Originally, polyphosphates, especially sodium triphosphate, were very successfully used for this purpose but, in view of their eutrophicating effect in water bodies, have not been able to be used at all, or only conditionally, for decades now. Another known example of builders which improve single-cycle washing performance is zeolite Na-A, which is known to be capable of forming such stable complexes with calcium ions in particular that their reaction with anions responsible for water hardness, particularly carbonate, to form insoluble compounds is suppressed. In addition, builders—particularly in laundry detergents—are supposed to prevent redeposition both of the soil detached from the fibers or generally from the surface to be cleaned and of insoluble compounds formed by reaction of cations responsible for water hardness with anions responsible for water hardness onto the cleaned fabric or surface. So-called co-builders, generally polymeric polycarboxylates, are normally used for this purpose. Besides their contribution to multiple-cycle washing performance, co-builders advantageously have a complexing effect towards the cations responsible for water hardness.
Besides the indispensable active components mentioned, such as surfactants and builders, detergents generally contain other components that are known collectively as washing aids and that encompass such diverse groups as foam regulators, redeposition inhibitors, bleaching agents, enzymes and dye transfer inhibitors. Particular importance is attributed to the bleaching agents, above all with regard to the boosting of washing or cleaning performance against a range of different soils. Auxiliaries such as these include substances that, in laundry detergents, support surfactant performance through the oxidative degradation of soils present on the fabric or soils present in the wash liquor after detachment from the fabric. The same also applies correspondingly to cleaning preparations for hard surfaces. Thus, inorganic peroxygen compounds, particularly hydrogen peroxide, and solid peroxygen compounds, which dissolve in water with release of hydogen peroxide or so-called active oxygen, such as sodium perborate and sodium carbonate perhydrate, have long been used as oxidizing agents for disinfection and bleaching purposes. Sodium carbonate perhydrate, which is often referred to in short as sodium percarbonate, is the addition compound of hydrogen peroxide onto sodium carbonate (empirical formula 2 Na2CO3—3 H2O2). The carbonate salts of the other alkali metals also form H2O2 addition compounds. In view of its often unsatisfactory storage stability in humid environments and in the presence of other typical detergent ingredients, particularly silicate-containing builders, the alkali metal percarbonate normally has to be stabilized against the loss of active oxygen. A key principle for stabilization is to provide the alkali metal percarbonate particles with a coating that may comprise one or more layers. Each coating layer may contain one or more inorganic and/or organic coating components.
Besides increasing storage stability, the presence of a coating generally alters the dissolving characteristics of the alkali metal percarbonate. For example, the high solubility of uncoated alkali metal percarbonates in water can have an adverse effect where they are present in enzyme-containing detergents/cleaning compositions, because relatively high concentrations of active oxygen are available just after the beginning of the washing or cleaning process and can impair the effect of a number of enzymes, including proteases. This impairment need not necessarily be attributed to the oxidative degradation (“denaturing”) of the enzyme, but may also arise from the fact that some soils (for example blood)—as substrates actually to be removed by the enzyme—are converted by the effect of the bleaching agent into a form which is less easy for the enzyme to attack. Accordingly, the object of coating the alkali metal percarbonate is to delay the release of the active oxygen.
Waterglass is known as a coating material for peroxygen compounds, particularly sodium perborate, from British Patent GB 174 891, according to which it is sprayed on as an aqueous solution and then dried for the purpose of increasing active oxygen stability. Waterglass, i.e. a mixture of alkali metal silicates, is also a coating component in Comparison Examples in the process according to German patent application DE 26 22 610. Here, a waterglass solution with a modulus (molar SiO2:Na2O ratio) of 3.3 is used. However, where thick coating layers are applied, the stabilizing effect is not good enough when percarbonate particles thus coated are stored in a phosphate-containing detergent powder, so that the document in question recommends the application of a combination of sodium carbonate, sodium sulfate and sodium silicate to the peroxo salt to be stabilized. According to U.S. Pat. No. 4,325,933, magnesium sulfate is also a suitable coating component. However, as is apparent from International patent application WO 95/02555 and European patent application EP 0 623 533, magnesium sulfate as sole coating component does not meet the necessary stability requirements. Accordingly, in addition to magnesium sulfate or a magnesium carboxylate, the coating of the alkali metal percarbonate particles described in those documents contains a salt from the group consisting of alkali metal carbonates, hydrogen carbonates and sulfates and, as a third component, an alkali metal silicate, the coating components mentioned being accommodated in one or more layers. It follows from European patent application EP 0 623 533 that the dissolving rate of coated sodium percarbonate particles decreases with increasing quantities of sodium silicate. International patent application WO 97/19890 teaches that sodium percarbonate with a single coating layer of essentially sodium sulfate has sufficient active oxygen stability at least when the sodium percarbonate core material is produced by fluidized-bed spray granulation. However, the dense particle structure only leads to a slightly lower dissolving rate of the sodium percarbonate.
European patent application EP 0 922 575 teaches the possibility of extending the dissolving time of sodium percarbonate through the presence of alkali metal silicate. Quantities of 0.5% by weight to 30% by weight of alkali metal silicate with a modulus of >3 and <5 are either mixed with sodium percarbonate or are applied thereto in the form of a coating layer. For example, the coating layer consists of 9% by weight sodium silicate. In addition, to improve active oxygen stability, special carboxylic acids or hydroxycarboxylic acids may be accommodated in one or more coating layers. Other known stabilizers from the group consisting of magnesium sulfate, sodium sulfate, sodium carbonate and sodium hydrogen carbonate may additionally be present in the coating layer. The sodium percarbonate particles thus coated are used in combination with enzymes above all for washing laundry or for dishwashing, although only preparations containing zeolite or sodium tripolyphosphate are actually disclosed.
Similarly, in the detergents according to International patent application WO 97/45524, which contain a cationic ester surfactant and an alkalinity system, which may even be sodium percarbonate, it is important that the alkalinity system is released slowly in water. A preferred coating for the slow release of sodium carbonate is said to be a coating containing sodium silicate with a modulus of 1.6 to 3.4 and, more particularly, 2.8. The sodium silicate may be replaced by magnesium silicate. The sodium percarbonate particles thus coated, which are described as slow-release particles, are used—partly together with sodium perborate—in preparations containing zeolite and/or sodium tripolyphosphate.
International patent application WO 96/22354 also describes detergents which contain sodium percarbonate particles coated with a combination of sodium carbonate, magnesium sulfate and sodium silicate. These particles dissolve in water more slowly than the detergent as a whole. They are used in zeolite-containing detergents.
It has now surprisingly been found that the bleaching effect of alkali metal percarbonate particles coated with a layer containing alkali metal silicate is developed particularly well if these alkali metal percarbonate particles are used in detergent or cleaning compositions that are free from water-insoluble builder, i.e. contain only water-soluble builder, phosphate builders being ruled out for ecological reasons, as mentioned above.